1. Field of the Invention
The present invention relates to an inkjet printer head. More particularly, the present invention relates to a printer head using a radio frequency micro-electromechanical system (RF MEMS) sprayer including an RF cavity resonator.
2. Background of the Related Art
In general, a spraying device for spraying a droplet of a liquid may be used in an inkjet printer head, a MEMS cooling device, or the like. A driving method for an inkjet printer head may be classified into a mechanical driving method using a piezoelectric element or a thermal driving method.
FIG. 1 illustrates a cross-sectional view of a conventional printer head using a piezoelectric element.
As shown in FIG. 1, a conventional printer head using a piezoelectric element includes a plate-shaped piezoelectric body 7, a vibrating plate 6 disposed under the piezoelectric body 7 for converting a longitudinally expanding motion of the piezoelectric body 7 into a bending motion, a liquid chamber layer 1 disposed under the vibrating plate 6 and including a liquid chamber 2 for storing ink, and a nozzle plate 5 having a nozzle 5a for spraying a droplet of ink and covering the liquid chamber layer 1. The nozzle plate 5 has may have a plurality of nozzles 5a each spaced at a predetermined distance interval.
The liquid chamber layer 1 is formed of a plurality of metal layers welded with pressure. The liquid chamber 2 for storing ink and a restrictor 3 for controlling a flow of ink are provided in the liquid chamber layer 1. The nozzle plate 5 having the plurality of nozzles 5a is positioned under the liquid chamber layer 1. The vibrating plate 6 is provided to cover a pressure chamber 4 above the liquid chamber layer 1. The restrictor 3 provides flow communication between the liquid chamber 2 and the pressure chamber 4. The nozzles 5a are connected to the pressure chamber 4. An electrode (not shown) for operating the piezoelectric body 7 is disposed above the vibrating plate 6.
When the piezoelectric body 7 is polled (i.e., generating an orientation in a piezoelectric body by applying an electric field to the piezoelectric body) to expand longitudinally, the vibrating plate 6 is bent and an inner pressure of the pressure chamber 4 increases to spray a droplet of ink outwardly through the nozzles 5a. While the droplet of ink is sprayed, the restrictor 3 blocks ink remaining in the pressure chamber 4 from flowing back into the liquid chamber 2. When the shape and position of the vibrating plate 6 are restored, the pressure chamber 4 is replenished with ink from the liquid chamber 2 through the restrictor 3.
To manufacture the vibrating plate 6, a green sheet is made of ZrO2. Then, holes of a predetermined size are bored into predetermined positions of the sheet. Subsequently, the sheet is heated to a high temperature, e.g., at least about 1,000° C. In addition, a lower electrode of an identical size is formed on the thin ZrO2 plate.
To manufacture the piezoelectric body 7, the ZrO2 plate with the lower electrode being formed thereon is screen-printed by precisely arraying a piezoelectric body paste. The piezoelectric body paste, having been screen-painted onto the ZrO2 plate, is then heated at a high temperature to form an upper electrode on the piezoelectric body 7.
A conventional inkjet printer head using the above-described piezoelectric body has a disadvantage of a low printing speed due to an operating speed limit of the piezoelectric body. In addition, such a conventional inkjet printer head has difficulty in controlling an amount of ink discharged. Further, the manufacturing process is complex and the structure is overly complicated thereby rendering high integration difficult.
In the alternate driving method of an inkjet printer head, i.e., the thermal driving method, heat is applied to a thin pipe so that an air bubble is generated to increase an inner pressure of the pipe. This increase in inner pressure causes the discharge of a liquid.
More specifically, a passage for ink is formed inside a semiconductor and a thermal resistor is disposed around the passage. Then, a current is applied to the resistor to cause the resistor to be heated and to generate an air bubble in the passage. The generated air bubble increases the inner pressure of the pipe thereby discharging ink from the pipe.
Output quality of an output device using an inkjet printer head varies severely according to ink quality and an amount of discharged ink. In printing a color image, if an amount of ink discharged is too great, then the printed image becomes dark overall, thereby lowering a resolution of the printed image.
Alternately, if an amount of ink discharged is too small, an output image becomes unclear or a quality of the image is degraded since some of the nozzles do not discharge any ink. Thus, a thermal driving inkjet printer head attempts to discharge ink adequately by regulating a voltage applied to the thermal resistor or a time for the heating.
The thermal driving inkjet printer head, however, is severely affected by ambient temperature and humidity conditions. Under high temperature and humidity conditions, such a printer head has problems in that an output image is too dark. Under low temperature and humidity conditions, ink is not discharged or an output image becomes unclear. Further, such a printer head has problems in that it is not easy to precisely regulate an amount of ink discharged and a discharging reaction rate of ink is low due to a limited operating reaction rate of the thermal resistor. Moreover, the printer head has additional problems in that the structure thereof is so complicated that it is not easy to highly integrate a plurality of nozzles, thereby further limiting the resolution of an output image.